LED package and fabricating method thereof

ABSTRACT

The invention provides an LED package capable of effectively releasing heat emitted from an LED chip out of the package and a fabrication method thereof. For this purpose, at least one groove is formed on an underside surface of the substrate to package the LED chip and the groove is filled with carbon nanotube material. In the LED package, a substrate having at least one groove on the underside surface is prepared. A plurality of electrodes are formed on a top surface of the substrate. Also, at least the one LED chip is mounted over the substrate to have both terminals electrically connected to the upper electrodes. In addition, carbon nanotube filler is filled in the groove of the substrate.

CLAIM OF PRIORITY

This application claims the benefit of Korean Patent Application No.2005-66010 filed on Jul. 20, 2005 in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting diode (LED) package,more particularly, which has at least one groove formed on an undersidesurface of a substrate to package the LED and filled with carbonnanotube (CNT) material so that heat transferred from an LED chip can beeffectively released out of the package, and a fabrication methodthereof.

2. Description of the Related Art

In general, a Light Emitting Diode (LED) converts into light an energygenerated by recombination of electrons and holes injected. The LEDincludes a red LED using GaAsP and a green LED using GaP. Also,recently, a nitride semiconductor using nitride such as GaN has beenhighlighted noticeably as a core material for opto-electronic materialsand electronic devices owing to its excellent physical and chemicalproperties. The nitride LED is capable of generating green, blue andeven ultraviolet ray light. Technical advancement has dramaticallyenhanced luminance of the nitride LED, which is thus rendered applicablein full-color sign boards and lighting devices, and the like. The LEDcan be packaged in various forms depending on its applications.

Meanwhile, when employed in an area requiring high-luminance such aslighting devices, the LED generates a massive amount of heat due toincrease in its power consumption. Such heat, if not effectivelyreleased out of the package, may potentially degrade properties of theLED and shorten useful life thereof.

To overcome the heat generation problems, conventionally, an LED packagewas installed with a heat releasing means using metal material with highthermal conductivity such as Cu, Al, and Ag. The metal material such asCu, Al, and Ag purportedly is low in thermal resistance and high inthermal conductivity. But the metal material is prone to oxidation inthe air, and suffers from void formation due to electron migrationresulting from a voltage impressed. These drawbacks prevent heat frombeing released effectively, thus undermining LED's operationalproperties and reliability.

SUMMARY OF THE INVENTION

The present invention has been made to solve the foregoing problems ofthe prior art and therefore an object according to certain embodimentsof the present invention is to provide an LED package which has at leastone groove formed in a package substrate and filled with high thermalconductivity carbon nanotube material to improve heat release propertiesthereof.

Another object according to certain embodiments of the present inventionis to provide a method for fabricating the LED package.

According to an aspect of the invention for realizing the object, thereis provided a light emitting diode package comprising: a substratehaving at least one groove formed on an underside surface thereof; aplurality of upper electrodes formed on a top surface of the substrate;at least one light emitting diode chip mounted over the substrate, thelight emitting diode chip having both terminals electrically connectedto the upper electrodes; and a carbon nanotube filler filled in thegroove of the substrate.

According to a certain embodiment of the invention, preferably, thesubstrate includes at least one via hole formed underneath the upperelectrodes to perforate the top and underside surfaces thereof. The viahole is filled with a conductive filler. Also, the light emitting diodepackage further comprises a plurality of lower electrodes formed on theunderside surface of the substrate to electrically connect to aconductive filler filled in the via hole.

According to a certain embodiment of the invention, the light emittingdiode package further comprises an insulating film formed on the top andunderside surfaces of the substrate, and inner walls of the groove andthe via hole.

Preferably, the insulating film comprises SiO₂, which can be formed onthe Si substrate via a simple process.

According to a certain embodiment of the invention, the light emittingdiode package further comprises a reflecting structure formed around thelight emitting diode chip mounted over the substrate, the reflectingstructure having an inclined surface for reflecting light emitted fromthe light emitting diode chip upwards. In addition, the light emittingdiode package further comprises a lens attached to the reflectingstructure over the light emitting diode, the lens controlling adirection of light emitted from the light emitting diode.

According to a certain embodiment of the invention, the groove is formedon the underside surface of the substrate in various configurations. Forexample, the groove comprises a plurality of holes extending from theunderside surface of the substrate toward the top surface of thesubstrate without perforating the substrate. Alternatively, the groovecomprises a plurality of slits extending from the underside surface ofthe substrate toward the top surface of the substrate withoutperforating the substrate.

According to another aspect of the invention for realizing the object,there is provided a method for fabricating a light emitting diodepackage comprising steps of:

-   -   preparing a substrate and a carbon nanotube paste;    -   forming a groove on an underside surface of the substrate;    -   filling the groove with the carbon nanotube paste;    -   forming a plurality of upper electrodes on a top surface of the        substrate; and    -   mounting at least one light emitting diode chip over the        substrate to electrically connect to the upper electrodes.

According to a certain embodiment of the invention, preferably, the stepof forming the groove comprises:

forming an insulating film on the top and underside surfaces of thesubstrate; partially removing the insulating film on the undersidesurface of the substrate and a lower part of the substrate to form atleast one groove; partially removing the insulating film on the top andunderside surfaces of the substrate and the substrate so that a via holeis formed underneath the upper electrodes to perforate the top andunderside surfaces of the substrate; forming an insulating film on innerwalls of the groove and the via hole; and filling a conductive filler inthe via hole.

At this time, preferably, the substrate comprises a Si substrate, andthe step of forming the insulating film on the top and undersidesurfaces of the substrate and the step of forming the insulating film onthe inner walls of the groove and the via hole comprise thermallytreating the Si substrate in an oxygen atmosphere to form a SiO₂insulating film on an exposed surface of the Si substrate.

According to a certain embodiment of the invention, preferably, the stepof preparing the carbon nanotube paste comprises:

mixing carbon nanotube powder with binder, solvent and dispersant at apredetermined rate; filtering the mixture; and aging the filteredmixture to complete the carbon nanotube paste.

According to a certain embodiment of the invention, the step of formingthe groove comprises forming a plurality of holes extending from theunderside surface of the substrate toward the top surface of thesubstrate without perforating the substrate. Alternatively, the step offorming the groove comprises:

-   -   forming a plurality of slits extending from the underside        surface of the substrate toward the top surface of the substrate        without perforating the substrate.

According to a certain embodiment of the invention, the step of fillingthe carbon nanotube paste comprises:

coating the carbon nanotube paste onto the groove of the substrate;filling the nanotube paste in the groove via screen printing or spincoating; and drying the filled carbon nanotube paste.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is vertical cross-sectional view illustrating an LED packageaccording to the invention;

FIGS. 2( a) to (c) are plan views illustrating configuration of a heatrelease means according to various embodiments of the invention; and

FIGS. 3( a) to (g) are cross-sectional views illustrating a method forfabricating an LED package according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. In thedrawings, the shapes and dimensions may be exaggerated for clarity, andthe same reference signs are used to designate the same or similarcomponents throughout.

FIG. 1 is a vertical cross-sectional view illustrating an LED packageaccording to a certain embodiment of the invention. Referring to FIG. 1,the LED package 10 according to the embodiment of the invention includesa substrate 11, a plurality of upper electrodes 12, an LED chip 21, andcarbon nanotube filler 13. The substrate 11 has a plurality of grooves gformed on an underside surface thereof. The upper electrodes 12 areformed on a top surface of the substrate 11. The LED chip 21 is mountedover the substrate and has both terminals electrically connected to theupper electrodes 12. Also, the carbon nanotube filler 13 is filled inthe grooves g of the substrate 11.

Moreover, according to this embodiment, the LED package further includesa reflecting structure 16 having an inclined surface i formed around theLED chip 21 mounted over the substrate 11. The inclined surface ireflects light emitted from the LED 21 upwards. Also, the LED packagefurther includes a lens 17 attached to the reflecting structure anddisposed over the LED chip 21. The lens 17 controls a direction of lightemitted from the LED chip 21.

The substrate 11 is exemplified by various general commercialsubstrates. For example, the substrate 11 is selected from a groupconsisting of an insulating ceramic substrate, a glass substrate or aconductive Si substrate, and a metal substrate. Especially the Sisubstrate is a commercial substrate widely utilized in manufacturing asemiconductor device. The Si substrate is cheap, easily processable andrelatively highly thermal conductive. This embodiment of the inventionemploys the Si substrate.

The substrate 11 includes grooves g formed on the underside surfacethereof and via holes h formed underneath the upper electrodes 12. Thevia hole h perforates the top and underside surfaces of the substrate.Preferably, the via hole h is filled with a conductive filler 15. Atthis time, the LED package may further include a plurality of lowerelectrodes 14 disposed on the underside of the substrate 11 andelectrically connected to the conductive filler 15 filled in the viahole h.

The conductive Si substrate, when adopted for the substrate 11, needs tohave an insulating film 111 disposed thereon before forming terminalsfor electrical connection so that it can mount an electrical devicethereon.

The insulating film 111 is formed to insulate the Si substrate that iselectrically conductive. The insulating film 111 is formed on a surface(top or underside) of the substrate 11 via a separate depositionprocess. Alternatively, the Si substrate is thermally treated in anoxygen atmosphere to form a SiO₂ insulating film having excellentinsulating properties. The Si substrate advantageously allows theinsulating film to be easily formed via a simple thermal treatmentprocess. The insulating film 111 is necessarily formed on the top andunderside surfaces of the substrate and also on inner walls of thegrooves g filled with the carbon nanotube filler and via holes h filledwith the conductive filler.

Meanwhile, preferably, the grooves g are formed on the underside surfaceof the substrate 11, below the LED 21 mounted over the substrate 11. Thegrooves g are filled with the carbon nantotube filler having superiorthermal conductivity. The grooves g allow heat generated in the LED 21to be easily discharged to the underside surface of the substratethrough the carbon nanotube filler 13.

The invention is characterized by filling the carbon nanotube filler 13in the grooves g to release heat. Carbon nanotube is a new tubular(cylindrical) material having hexagons of six carbons connected with oneanother into the form of a tube (cylinder). The carbon nanotube is namedas such due to its diameter of mere up to several nanometers. The carbonnanotube has electrical conductivity similar to that of copper, thermalconductivity similar to that of diamond, the highest in the naturalworld and strength ten thousand times that of steel. Carbon fiber, iftransformed only 1%, is breakable. But the carbon nanotube is durableeven if transformed 15%. The carbon nanotube has tensile force superiorto that of diamond. There is a prospect that the carbon nanotube iswidely used for materials for the high-tech electronics industry anddaily life. Also, the carbon nanotube is applicable infinitely accordingto development of related technologies, as exemplified by thin CathodRay Tube (CRT) consuming extremely little power, alternative materialsfor bulbs, ultrahigh strength fiber such as spacesuits, mobile phonebattery, hydrogen fuel cell, sensor, and the like.

As described above, the carbon nanotube exhibits very excellent thermalconductivity. In comparison with Cu (about 400 W/mK of thermalconductivity) and AI (about 203 W/mK of thermal conductivity) known tohave high thermal conductivity, the carbon nanotube has a very highthermal conductivity of about 3000 W/mK at a temperature of 100K or moreand about 3700 W/mK at a temperature of 100K or less. Therefore, thisallows heat to be effectively released out of the LED package.

The grooves g filled with the carbon nanotube filler 13 may be formed invarious configurations. FIG. 2 illustrates various configurations of thegrooves. FIGS. 2( a) to (c) are bottom plan views illustrating an LEDpackage according to various embodiments of the invention. First, asshown in FIG. 2( a), the grooves g are configured as a plurality ofholes extending from an underside surface of a substrate 11 toward a topsurface of the substrate 11 without perforating the substrate 11. Incase where the grooves g perforate the substrate 11, the carbon nanotubefiller filled in the grooves and a wiring structure formed thereon maybe electrically short-circuited with each other. Thus, preferably, thegrooves g do not perforate the substrate 11.

Further, as shown in FIG. 2( b), the grooves g are configured as aplurality of slits extending toward the top surface of the substrate 11without perforating the substrate 11.

Also, as shown in FIG. 2( c), the groove g may be configured as a largehemispheric structure.

The variously structured grooves as just described are applicable to theinvention. But given adherence of the carbon nanotube filler 13 filledin the grooves g onto the substrate 11, in case where the carbonnanotube is filled in the single big groove as shown in FIG. 2( c), itsweight may separate the nanotube filler 23 from the substrate 11.Therefore, preferably, the grooves are structured (hole structure orslit structure) to have a small sectional area as in FIGS. 2( a) to (b)and then filled with the carbon nanotube filler.

Referring back to FIG. 1, the substrate 11 or the insulating film 111has the plurality of upper electrodes 12 electrically connected to theLED 21. The upper electrodes 12 each are connected to an anode terminaland a cathode terminal to supply current from the outside to the LED 21.FIG. 1 illustrates the single LED chip 21 mounted in the LED package butalternatively a plurality of LED chips may be mounted therein. Thus, thenumber of the upper electrodes 12 can be varied adequately by the numberof the LED chips 21. To be electrically connected to the outside of theLED package, the upper electrodes 12 are electrically connected to theconductive filler 15 filled in the via hole h formed thereunderneath,and the conductive filler 15 filled in the via hole h is electricallyconnected to lower electrodes 14 formed on the underside surface of thesubstrate 11. The lower electrodes 14, when supplied with current fromthe outside, transfers it through the via hole h and upper electrodes 12to the LED chip 21.

FIG. 1 illustrates a structure in which the upper electrodes 12 andlower electrodes 14 are connected each other through the conductivefiller 15 filled in the via hole h. The invention however is not limitedthereto. Alternatively, the upper electrodes 12 each may extend to aside and underside of the substrate to be connected to the lowerelectrodes 14 each without the via hole h employed.

Furthermore, FIG. 1 illustrates the LED 21 chip flip-bonded to the upperelectrodes 12 via a conductive bump. But the invention is not limitedthereto. The LED chip 21 can be mounted over the substrate 11 via avariety of methods known in the art.

According to this embodiment, additionally, the LED package furtherincludes a reflecting structure 16 having an inclined surface i formedaround the LED chip 21 mounted over the substrate 11. The inclinedsurface i reflects light emitted from the LED chip 21 upwards. Thereflecting structure 16 is made of a material equal to that of thesubstrate 11 and may surround the LED 21. The reflecting structure 16around the LED chip 21 has sides thereof inclined toward the LED chip 21to form the inclined surface i. The inclined surface i is coated withhigh-reflective material. Thus, light emitted from the LED chip 21 tothe inclined surface i is reflected upwards, thereby enhancingefficiency of light exiting from the LED package 10.

Moreover, a lens 17 may be disposed over the LED chip 21 from whichlight is emitted so that it can control a direction of light. The lens17 may include a plate made of glass and a micro-optics (notillustrated) of a micro lens structure formed on the glass plate. Themicro-optics reflects or refracts light emitted from the underlying LEDchip 21 to control light to be generated in a desired direction from theLED package 10. Also, the lens is attached to a top surface of thereflecting structure, thereby protecting the LED chip 21 from externaleffects.

Further, the invention provides a fabrication method of the LED packageas just described.

FIG. 3 illustrates in a stepwise fashion a method for fabricating theLED package according to an embodiment of the invention. The embodimentemploys a Si substrate, which thus necessitate a process of forming aninsulating film thereon. But such a process is omissible when aninsulating substrate is adopted.

First, referring to FIG. 3( a), a substrate 11 is prepared and aninsulating film 111 is formed on a top surface and an underside surfacethereof. To form the insulating film 111, a material such as SiO₂ isdeposited. Alternatively, a Si substrate is thermally treated in anoxygen atmosphere.

Next, as shown in FIG. 3( b), the insulating film 111 on the undersidesurface of the substrate 11 and the substrate 11 are partially removedto form grooves g. Preferably, the grooves g are formed on the undersidesurface of the substrate 11, below an LED chip mounted. The grooves gmay be formed in various structures via mechanical drilling and chemicaletching. For example, the grooves may be structured as a plurality ofholes extending from the underside surface of the substrate 11 towardthe top surface thereof without perforating the substrate 11.Alternatively, the grooves g may be structured as a plurality of slitsextending from the underside surface of the substrate 11 toward the topsurface thereof without perforating the substrate 11.

Then, as shown in FIG. 3( c), the insulating film 111 and the substrate11 are partially removed so that via holes h are formed to perforate thetop and underside surfaces of the substrate 11.

Thereafter, as shown in FIG. 3( d), the insulating film 111 is formed oninner walls of the grooves g and via holes h. To form the insulatingfilm 111, as shown in FIG. 3( a), a material such as SiO₂ is depositedor the Si substrate is thermally treated in an oxygen atmosphere.Especially it is preferable to form a SiO₂ insulating film, which is athermal oxide film, via thermal treatment. This thereby allows theinsulating film to be formed even on inner walls of the grooves g andvia holes h which have a small diameter.

Then, as shown in FIG. 3( e), the via holes (reference sign h of FIG. 3(d)) are filled with conductive filler 15. Then upper electrodes areformed on a top surface of the substrate 11 or the insulating film 111to electrically connect to the conductive filler 13 filled in the viaholes. Also, a nanotube filler 13 is filled in the grooves (referencesign g of FIG. 3( d)) formed on the underside of the substrate 11.

The carbon nanotube filler 13 is formed in a paste to be filled in thegrooves. To form the carbon nanotube paste, a carbon nanotube powder ismixed with binder, solvent and dispersant at a predetermined rate. Then,the mixture is filtered and the filtered mixture is aged to complete thecarbon nanotube paste. To obtain the carbon nanotube paste, 40 to 50 wt% of carbon nanotube powder, 20 to 30 wt % of binder, 20 to 30 wt % ofsolvent and 2 to 5 wt % of dispersant are mixed. Examples of thenanotube powder include a single wall or multiwall carbon nanotubepowder. Examples of the binder include Poly Vinyl Butyral, EthylCellulose, Polyester, Poly Acrylate, Poly Vinyl Pyrrolidone, and thelike. Examples of the solvent include Ethyl Alcohol, Toluene, or amixture of Ethyl Alcohol and Toluene. Also, examples of the dispersantinclude Glycerine, Oilfish and Dioctyl Phtahalate (DOP).

Further, to fill the carbon nanotube paste in the grooves, the carbonnano tube paste is coated onto the grooves formed on the undersidesurface of the substrate. Then, the carbon nanotube paste is filled inthe grooves via screen printing or spin coating. In addition, the filledcarbon nantotube paste is dried.

Then, as shown in FIG. 3( f), at least one LED chip 21 is mounted overthe substrate 11 to electrically connect to the upper electrodes 12. TheLED chip 21 can be disposed via various LED bonding methods known in theart. By way of an example, FIG. 3 illustrates the LED chip 21flip-bonded to the upper electrodes 12 via a conductive bump and thusmounted over the substrate 11 to electrically connect to the upperelectrodes 12. Alternatively, the LED chip 21 is solder bonded onto thesubstrate 11 or bonded thereonto via binder. Alternatively, the LED chip21 has both terminals wire-bonded to the respective upper electrodes 12.Of course, the LED 21 may have one terminal bonded to one upperelectrode and the other terminal wire-bonded to the other upperelectrode.

Finally, as shown in FIG. 3( g), a reflecting structure 16 having aninclined surface i is disposed around the LED chip 21 over the substrate11. The inclined surface i reflects light emitted from the LED chip 21upwards. A lens 17 is disposed over the LED chip 21 to control thedirection of light emitted from the LED chip 21. Also, lower electrodes14 are formed on the underside surface of the substrate 11 toelectrically connect to the conductive filler filled in the via holes,thereby completing fabrication of the LED package.

In this fashion, the invention employs carbon nanotube material withhigh thermal conductivity to release heat. Consequently, heat emittedfrom the LED chip of the LED package can be effectively released out ofthe package.

As set forth above, according to preferred embodiments of the invention,carbon nanotube material with high thermal conductivity is filled,thereby allowing heat emitted from an LED chip of an LED package to beeffectively released out of the package. This prevents any change inoutput properties of the LED chip and improves useful life andreliability thereof.

While the present invention has been shown and described in connectionwith the preferred embodiments, it will be apparent to those skilled inthe art that modifications and variations can be made without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

1. A light emitting diode package comprising: a substrate having atleast one groove formed on an underside surface thereof; a plurality ofupper electrodes formed on a top surface of the substrate; at least onelight emitting diode chip mounted over the substrate, the light emittingdiode chip having both terminals electrically connected to the upperelectrodes; and a carbon nanotube filler filled in the groove of thesubstrate.
 2. The light emitting diode package according to claim 1,wherein the substrate includes at least one via hole formed underneaththe upper electrodes to perforate the top and underside surfacesthereof, the via hole be filled with a conductive filler.
 3. The lightemitting diode package according to claim 2, further comprising aplurality of lower electrodes formed on the underside surface of thesubstrate to electrically connect to a conductive filler filled in thevia hole.
 4. The light emitting diode package according to claim 2,further comprising an insulating film formed on the top and undersidesurfaces of the substrate, and inner walls of the groove and the viahole.
 5. The light emitting diode package according to claim 4, whereinthe insulating film comprises SiO₂.
 6. The light emitting diode packageaccording to claim 1, further comprising a reflecting structure formedaround the light emitting diode chip mounted over the substrate, thereflecting structure having an inclined surface for reflecting lightemitted from the light emitting diode chip upwards.
 7. The lightemitting diode package according to claim 6, further comprising a lensattached to the reflecting structure over the light emitting diode, thelens controlling a direction of light emitted from the light emittingdiode.
 8. The light emitting diode package according to claim 1, whereinthe groove comprises a plurality of holes extending from the undersidesurface of the substrate toward the top surface of the substrate withoutperforating the substrate.
 9. The light emitting diode package accordingto claim 1, wherein the groove comprises a plurality of slits extendingfrom the underside surface of the substrate toward the top surface ofthe substrate without perforating the substrate.